A wide variety of devices may be damaged if operation continues at temperatures above ordinary operating temperatures. For example, the rolling bearings on railway cars experience an increased operating temperature as the bearing begins to fail (due to any number of reasons). Due to the large number of such bearings on a train and the harsh environment to which such bearings are exposed, it is difficult to monitor such bearings.
In order to determine if a bearing of a railway car is overheating, there have been disclosed specially adapted bolts which are used in place of one of the normal securing bolts for the end cap of the bearing. Such special bolts react when a predetermined temperature is reached, typically when the temperature of a fusible element of the bolt melts. For example, in U.S. Pat. No. 4,818,119 (Busch et al.), there is disclosed a bolt in which a spring biased pin is ejected from a head of the bolt when a fusible alloy in which the spring is embedded melts. The bolt includes a sealing closure plug which is forcibly removed by the ejecting pin.
Other temperature signalling devices have also been disclosed in the prior art. For example, in U.S. Pat. No. 3,548,780 (Kliewer), a food temperature signalling device is disclosed for signalling when a food article is sufficiently cooked (warmed). In this device, a spring biases a retaining rod toward a fusible plug. The retaining rod moves into the plug when the melting temperature is reached, and this movement releases a signalling staff. Other devices of a similar nature are disclosed in the following U.S. Pat. No. 4,748,931 (Volk), stem head buried in a fusible material; U.S. Pat. No. 4,356,790 (Gee), fusible thin film used as a bonding material; U.S. Pat. No. 3,280,629 (Kliewer), fusible plug; and U.S. Pat. No. 1,509,110 (Potter), fusible links.
Safety devices have also been disclosed in the prior art for protecting against extreme conditions and relieving such conditions when they are experienced. For example, in U.S. Pat. No. 4,365,643 (Masclet et al.), a fuse device for a pneumatic tire is used to vent the pressure in the tire if a certain pressure (which can be related to temperature) is exceeded. In the disclosed device, a central piston blocks escape of the tire pressure, and the tire pressure acts as an upward force on this piston. The piston is prevented from moving by an annular disc of eutectic (fusible) material. When the pressure in the tire exceeds the desired pressure, the eutectic material breaks up and releases the pressure. It will be appreciated that the eutectic material also breaks up more easily at higher temperatures, so that if the tire is heating up as the pressure increases (i.e., because of braking of the tire), the eutectic material breaks up sooner to more quickly prevent the (rising) pressure in the tire from exceeding a desired pressure.